Buzz
Today, the diazotype technique is widely used for blueprinting, creating dark lines on a white surface. This method is the go-to for reproducing large-scale drawings.
Doug Menuez/Getty ImagesMain Points to Remember
- Blueprints are oversized architectural and construction plans.
- The traditional blueprinting technique, developed in 1842, relies on a light-sensitive chemical process to generate a negative image (blue lines on a dark background). In contrast, the contemporary diazotype approach creates dark lines on a white surface.
If you’ve ever observed a house under construction or witnessed an extension being added to a home, you’re likely familiar with blueprints. These large sheets of paper serve as the primary means of communication in construction projects. Blueprinting is the conventional way to duplicate extensive architectural and construction plans. Originally, blueprints featured white lines on a blue base, but modern methods now produce blue lines on a white background.
The word "blueprint" typically refers to two distinct printing techniques: the traditional blueprint and the diazotype method.
Blueprinting, the older of the two methods, was developed in 1842. In this process, a translucent paper with the original drawing is placed over paper treated with ferric ammonium citrate and potassium ferricyanide. When exposed to light, the chemicals react in areas not covered by the drawing, creating a blue hue. After exposure, the paper is rinsed in water, resulting in a negative image where the drawing appears white against a deep blue backdrop.
The diazotype technique involves coating paper with a light-sensitive mixture containing a diazonium salt, a reactant, and an acid to prevent premature reactions. The original semi-transparent drawing is placed over the treated paper, and a same-sized copy is produced through direct contact. Light exposure breaks down the diazonium salt. Ammonia gas or solution is then applied as a developer, neutralizing the acid and enabling the remaining diazonium salt to react with the reactant, forming a blue dye. This process creates dark lines on a white background, making it the preferred method for reproducing large-format drawings today.
Blueprints remain in use due to their cost-effectiveness. The diazotype method is far more affordable than investing in large-format copying machines, making it a practical choice for many.
